regained control of their movements, and 

 escaped. 



The water of the Kvichak was found to 

 be very soft and highly resistant, having a 

 measured resistance of 41,000 ohms per 

 centimeter cube. It was found that in such 

 highly resistant water, the line between 

 over-control (that is, immediate narcosis 

 without electrotaxis) and optimum control 

 was so fine that it was not possible to 

 ascertain it exactly under the conditions 

 of this experimental operation. 



Optimum Shocker Site Characteristics 



As evidenced by the different efficiencies 

 achieved at the two experimental sites, 

 the characteristics of an electrofishing 

 installation can have an appreciable effect 

 on the efficiency of collection. In this 

 respect, the second site appeared almost 

 optimum. The characteristics of a good 

 shocker site are as follows: 



1. Current: Fast enough in the main 

 river to cause the migrating fish to choose 

 a narrow path fairly close to shore in 

 slower water. A sharp "edge" between 

 fast and slow water is desired. 



2. Depth: The depth at the path of 

 migration should not be over 5 feet, the 

 bottom sloping upwards toward shore so 

 that the positive electrode is in water 

 not greater than 3 feet. If the positive 

 electrode is positioned just under the 

 surface, it is suspected that the location 

 would not be too critical: up to a 10 -foot 

 maximum depth. 



3. Conductivity: As high as possible; 

 but since little can be done about this 

 within a given river system, it must be 

 accepted as an independent characteristic. 



4. Observation: A fairly high bank 

 downstream from the shocker site would 

 facilitate observation for the tagged fish; 

 otherwise, an elevated platform should be 

 constructed from 50 to 100 yards down- 

 stream. 



DISCUSSION 



The experimental operations described 

 here have indicated some feasibility in 

 capturing tagged or individually identi- 

 fiable fish from a migrating school of 

 red salmon. 



The apparatus was originally developed 

 for a quite different purpose than the use 

 to which it was put in this experiment. 

 Crude field adaptations for the electrode 

 system were made using available mate- 

 rials. Refinements in the equipment, based 

 on experience achieved during this field 

 operation, could substantially improve 

 efficiency. The increment in efficiency of 

 the operation at Site No. 2 over Site No. 1 

 indicated how field experience could im- 

 prove the selection of location, installa- 

 tion of the gear, and techniques of opera- 

 tion. Additional experience and improved 

 electrode systems should further increase 

 the ability of the apparatus to capture 

 tagged salmon. Sections of expanded 

 aluminum screening, perhaps lightly 

 anodized and dyed a full color for cam- 

 ouflage, would make better electrodes 

 than the materials used. Three or four of 

 these 4- by 8-foot panels linked together 

 would serve as a negative electrode, and 

 1, or possibly 1/2 of a section, as the 

 positive electrode. 



It might also be better to suspend the 

 positive electrodes just under the surface 

 of the water by floats or a supporting 

 framework, rather than on the stream 

 bottom. An electrode in contact with the 

 bottonn allows much of the current to 

 pass, through the streambed, where it has 

 no effect on the fish. Having the positive 

 electrode suspended closer to the surface 

 could also serve to bring the fish into a 

 better position for netting. Such installa- 

 tion of the electrode, even though it would 

 be more visible to the fish, should not 

 have a frightening effect on the fish. Float- 

 ing A-frames on the river surface, used 

 as "ripple dampeners", for improving 

 visibility fronn the counting towers, had 

 no effect on the passage of fish. Moored 

 boats and floats adjacent to the migration 

 path were observed to have no effect on 

 the fish passing close by, as long as these 

 objects were stationary. Moving objects 

 frightened the fish, but man-made sta- 

 tonary objects, even brightly colored or 

 shiny, had no effect on the passage of 

 fish. In fact, during the important parts of 

 the run, fish appear to be oblivious to all 

 objects around them.* 



The use of electrofishing methods to 

 capture specific fish in Bristol Bay rivers 



4 Thompson, W. F., andD. W. Clancy. 1959. Length nneasure- 

 ment of migrating salmon by paired underwater cameras. 

 Photogrammetric Engineer, vol. 25, No. 3 (June), pp. 449-455. 



